This invention relates to a tilting centrifugal casting machine used for casting compound rolling rolls.
For obtaining a rolling roll having both wear and break resistance, it needs to form a compound roll by integrally joining together a high-hardness shell layer and a high-toughness inner layer, and centrifugal casting is most suitable for producing such compound rolls. There have been known several types of methods for producing compound solid rolls according to such centrifugal casting techniques as shown in the following:
1. A method in which first the shell layer alone is formed by centrifugal casting, then the mold is erected and molten metal for forming the inner layer is poured into the mold to form a solid structure; PA1 2. A method in which parts of the shell layer and partial inner layer are formed by centrifugal casting, then the mold is erected and molten metal for forming the inner layer is poured thereinto to thereby make a solid structure; PA1 3. A vertical centrifugal casting method in which the mold is arranged such that its axis of rotation will be vertical, and then both shell and inner layers are formed by centrifugal casting; PA1 4. A special centrifugal casting method in which the axis of rotation of the mold is arranged horizontal and, after forming the shell layer, said axis of rotation is gradually shifted to its vertical position which successively pouring molten metal for the inner layer to thereby make a solid body; and PA1 5. A tilting centrifugal casting method in which the axis of rotation of the mold is tilted at a certain given angle and both shell and inner layers are formed by centrifugal casting to make a solid structure on the centrifugal casting machine.
However, all of these methods have their own drawbacks and attendant problems. For example, the methods of (1) and (2) necessitates use of a specific solvent or the like and also skilled techniques are required for welding. The method of (3) is unsuited for casting of elongated articles such as rolls, while the method of (4) necessitates enlargement of the equipments proportionally to the increase of roll weight and hence is unsuited for industrial use.
The method of (5) is best of the known centrifugal casting methods. According to this method, the above-said problems accompanying the methods of (1) to (4) are solved. That is, the equipment cost is low and no specific welding techniques are required. Further, the component and structure variation occurring in a range from an outer layer to an inner layer can be freely controlled, allowing reduction of the residual stress, increase of strength at the boundary between the outer and inner layers, and the improvement of anti-spalling property (resistivity against rupture caused by the impact) of the outer layer and of the structure of the inner layer.
In a centrifugal casting machine for producing rolls, large centrifugal force is required for obtaining a sound and particularly segregation-free shell, and for this purpose, the mold must be rotated at high speed. It is, on the other hand, of great importance to minimize vibration of the mold for ensuring safety of the casting machine and for obtaining a roll of good quality. This requirement for high speed rotation and that for minimization of mold vibration are the contradictory matters. Heretofore, many efforts and attempts have been made mainly for achieving improvement of the mold by eliminating its strain or improvement of casting machine by increasing its rigidity or by using rollers having a specific vibration-damping means. However, these are not sufficient to obtain satisfactory vibration damping effect. This problem is serious particularly in the method of (5) where the gross weight of the machine including the mold supplied with the molten metal amounts to 3 to 4 times the roll weight as both shell and inner layer are formed by centrifugal casting to make a solid structure on the centrifugal casting machine.